Investment casting wax

ABSTRACT

AN IMPROVED INVESTMENT CASTING WAX COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 35-65 WEIGHT PERCENT REFINED PETROLEUM WAX, SOLID CHLORONATED POLYPHENYL, ACID TYPE MONTAN WAX AND STEARIC ACID. SAID COMPOSITION HAS THE ADVANTAGE OF LOW SHRINKAGE, LOW PENETRATION AND RAPID SET UP.

United States Patent Oflice 3,667,979 Patented June 6, 1972 3,667,979 INVESTMENT CASTING WAX John C. Merges, Jr., Glen Mills, and Richard E. Ware,

Trainer, Pa., assignors to Sun Oil Company, Philadelphia, Pa. No Drawing. Filed Apr. 30, 1971, Ser. No. 139,243 Int. Cl. C08h 9/10 US. Cl. 106268 16 Claims ABSTRACT OF THE DISCLOSURE An improved investment casting wax composition consisting essentially of about 35-65 weight percent refined petroleum wax, solid chloronated polyphenyl, acid type montan wax and stearic acid. Said composition has the advantage of low shrinkage, low penetration and rapid set up.

CROSS-REFERENCE TO RELATED APPLICATIONS This invention is related to that described and claimed in applicants application Ser. No. 139,819, filed the same date as this application, and constitutes another improved investment casting wax containing a substantial amount of petroleum wax.

BACKGROUND OF THE INVENTION This invention relates to an investment casting wax. More specifically, it relates to an investment casting wax containing a major amount of petroleum wax and smaller amounts of other materials. These materials are a solid chlorinated polyphenyl, acid type montan wax and stearic acid. The resulting composition, despite the large amount of petroleum wax, has low shrinkage, low penetration and other properties which give it utility as an investment casting wax.

Investment casting refers to a method of quantity production of parts, usually having an intricate shape. The parts are normally metal, e.g., brass, steel, Zinc or lead and alloys thereof. The advantages of this method, for example, over ordinary sand casting, is that the metal part has an exceptionally good surface, sharp outline, and dimensional accuracy. Another advantage is that a metal part having dimensional accuracy and/or with an intricate shape is obtained without further machining.

In the simplest form of investment casting, a wax replica is made of the part to be reproduced. The wax replica is coated over or invested with a ceramic forming material, e.g., a sand-magnesia mixture. After the investment sets the wax replica invested with the sandmagnesia mixture is heated to melt out the wax and then baked to fuse the sand-magnesia. The wax may be reused. After cooling, the resulting ceramic mold is strong enough to support the molten metal poured into the cavity of the mold. The hot metal is poured into the top vent of the mold; a bottom vent allows for air to escape. After the metal solidifies and cools, the cooled ceramic mold is removed, normally by breaking it away from the metal part. The metal reproduction usually needs no further machining except to trim ofl? the metal that solidified in the vents.

To produce the aforementioned wax replica, a die is required to make repetitions of the wax replica. This die, usually of metal, is machined or cast to match the part to be reproduced with precision. Into the cavity of this die the investment casting wax, as a slush, is injected. After cooling, the solid wax replica is removed from. the die. This wax replica has the strength to be handled and invested, and when melted out of the ceramic investment, leaves behind little or nil ash which otherwise would cause imperfections on the surface of the metal reproduction.

An investment casting wax normally contains hard naturally occurring waxes such as candelilla or carnau'ba or mixtures of these waxes, said waxes having shar-p melting points, with various resins. A petroleum wax may be present in the investment casting wax but only as a small percentage of the total blend.

Petroleum wax has not been extensively used in any commercial casting wax since it undergoes a marked volume change as it goes through its melting point and softens gradually up to its melting point. The converse, i.e.; a gradual hardening of the petroleum wax as its temperature becomes less than its melting point, is also a problem. This gradual hardening is often referred to as slow setup. The disadvantage of a slow setup is that a substantial amount of time has to elapse before the wax becomes hard enough to be handled without damaging. By comparison, an operable investment casting wax has a rapid setup.

An article in a British trade journal, Foundry Trade Journal, December 1962, Pattern Waxes for Investment Castings by I. H. W. Booth, describes in greater depth the volume change of a petroleum wax. For example, it states that the expansion of a typical paraffin wax from F. to its melting point is about 14%. Also, a petroleum wax is usually too soft at an elevated temperature, e.g., -1 10 F., to be used in the investment casting method. The ideal investment casting wax would undergo no volume change as it goes through its melting point. Also, the ideal casting wax would remain hard at elevated temperatures which are below its melting point.

SUMMARY OF THE INVENTION The present invention is an improved investment casting wax composition consisting essentially of about 35-65 weight percent of petroleum wax, 25-55 weight percent of solid chlorinated polyphenyl, 5-15 weight percent of acid type montan wax and 0.1-5.0 weight percent of stearic acid. The petroleum wax can be a parafiin or a microcrystalline wax or mixtures thereof. Despite the substantial quantity of petroleum wax, this improved investment casting wax has low shrinkage and low penetration as well as other desirable properties. The present invention also relates to a wax replica comprising the aforementioned wax composition.

DESCRIPTION A refined petroleum wax can be classified by the processes used to prepare the wax. These processes; i.e., distillation, solvent extraction, clay treating, hydrotreating, etc., are described in great detail in Chapter of The Chemistry and Technology of Waxes, Albin H. Warth, Library of Congress, Catalog Card Number: 56- 6695. A refined petroleum wax prepared by these processes can be a component of the investment casting wax composition defined herein.

A refined petroleum wax can be also classified by the relative size of the wax crystals. A macro crystal wax is normally referred to as paraffin wax; a micro crystal wax is normally referred to as a microcrystalline wax. These classes are defined in greater depth in the aforementioned reference. Paraffin wax or microcrystalline waxor 'mixtures thereof can be used as a component of the investment casting wax composition defined herein.

'Refined paraflin waxes are available with a wide range of physical properties, e.g., melting points can be as low as 100 -F. (AMP) or as high as 160 F. (AM'P). While the lower melting point waxes can be used with this invention, it is preferred to use those paraflin waxes having a melting point in excess 'of 127 F. (AMP) and more preferable in excess of 129 -F. (AMP). AMP refers to the American Melting Point which is an arbitrary 3 F. higher than the ASTM melting point. A preferred paraffin wax melting point range is 130 F.-156 F. (AMP). Penetration values at 77 F. (ASTM D-1321) for paraffin waxes range from 40 to 5. A preferred penetration at 77 F. is less than 33; a more preferable penetration is less than 15. A preferred penetration at 77 F. range is 15-7. A highly preferred refined paraflin wax would be one having a melting point of 130 F.-1'56 F. (AMP) and a penetration at 77 F. of 15-7.

Microcrystalline waxes are available with a wide range of physical properties; for example, melting points can be as low as 140 F. oras high as 200 F. While the lower melting point microcrystalline waxes can be used with this invention, it is preferred to use those microcrystalline waxes having a melting point in excess of 151 F. and more preferably in excess of 175 F. A preferred microcrystalline melting point range is 175 F.-'197 F. The melting point temperatures for the microcrystalline waxes are determined by ASTM D-127. Penetration values at 77 F. (ASTM D-1321) for microcrystalline wax range from 25 to 3. A preferred penetration at 77 F. is less than 2]; a more preferred penetration is less than 12. A preferred penetration at 77 F. range is 13-4. A highly preferred microcrystalline wax would be one having a melting point of 175 F.-197 F. and a penetration at 7 7 F. of 13-4.

The refined petroleum wax used in this invention can be a parafiin wax or a microcrystalline wax or mixtures thereof. While the weight ratio of microcrystalline wax to paraffin wax can range from 0 to 100, it is preferable that some microcrystalline wax be used. A preferred weight ratio range of microcrystalline wax to paraflin wax is 0.05-1.0. A more preferable ratio is 0.2 to 0.60.

The term paraffin wax or microcrystalline wax, as used herein, refers to a wax having a narrow boiling range, a broad boiling range, a mixture of 2 or more narrow boiling range waxes, or a mixture of narrow and broad boiling ranges, etc.

Generally, the amount of petroleum wax presented in the investment casting wax defined herein will be about 35-65 weight percent. A preferred range is about 40- 60%; a more preferable range is about 45-55%.

Chlorinated polyphenyl refers to chlorinated biphenyl, terphenyls, higher polyphenyls and mixtures thereof. Normally, the commercial chlorinated polyphenyls are mixtures of chlorinated components rather than the individual isomers. Methods for preparing these chlorinated materials, and physical and chemical properties of these chlorinated materials, are described in volume 5, Kirk-Othmer Encyclopedia of Chemical Technology, 2nd edition, starting at page 289. These chlorinated materials are available as either liquids or solids at room temperature; however, only those chlorinated polyphenyls which are solid at room temperature are satisfactory as a component of the improved investment casting wax defined herein.

The amount of solid chlorinated polyphenyl admixed with the other components of the investment casting wax defined herein can constitute about 25-55 weight percent of the total. Preferably, the solid chlorinated polyphenyl constitutes about 35-45 weight percent of the total.

Typical range of physical properties for a suitable solid chlorinated polyphenyl is as follows: specific gravity 1.470-'l.8l1 (25/25 C.); acidity 0..14-1.4 (maximum mgm. KOH/gm.).

Acid type montan wax refers to a portion of mineral wax, the latter extracted from brown coals or lignites. After the crude montan wax has been extracted, it is refined by known processes to remove the resinous and 'asphaltic materials. A typical refined montan wax contains about 60-70% esters, 20-30% wax acids in the C -C range, and minor amounts of free alcohols, ketones and resins not entirely removed by ordinary purification.

The various processes for separating into or converting the solid refined montan wax into an acid type montan wax is described in the aforementioned text by Warth, Chapter 4, and in Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd edition, volume 22, Waxes, pages 168-169, also volume 12, Lignite and Brown Coal, pages 406-409.

The amount of aci dtype montan wax admixed with the other components of the investment wax defined herein can constitute about 5-15 weight percent of the total. Preferably, the acid type montan wax constitutes about 8-12 weight percent of the total. Ranges of typical properties of an acid type montan wax, which are satisfactory as components of the casting wax, are as follows: melting point of 170-185 F.; acid value of (ASTM D-1386-557); saponification value of 130- 180 (ASTM D-1387-557); and ester value of 15-30. A typical acid type montan wax can also be defined as a egg-C32 carboxyl acid.

The amount of stearic acid admixed with the other components of the investment wax defined herein can constitute about 0.1-5.0 weight percent of the total weight. Preferably, the stearic acid constitutes about 1-3 weight percent of the total weight.

The components of the investment casting wax defined herein are uniformly distributed throughout the petroleum wax. Conventional processing can be used to achieve this uniform distribution.

The following examples illustrate this invention.

EXAMPLES A typical microcrystalline wax, used along with the other components mentioned herein for illustrative purposes, had a melting point of F. (ASTM D- 12-7), a viscosity at 210 F. of 84 SUS, a penetration at 77 F. of 5 and an oil content of 0.4%. One typical parafiin wax, had a melting point of 156 F. (AMP), a viscosity at 210 F. of 44.8 SUS, a penetration at 77 F. of 9 and an oil content of 0.2%. Another typical paraffin wax had a melting point of 145 F. (AMP), a viscosity at 210 F. of 40 SUS, a penetration at 77 F. of 9 and an oil content of 0.2%. The chlorinated polyphenyl had a softening point of 208-222 F. and a specific gravity at 25 C./25 C. of 1.670. The stearic acid used was a readily available commercial grade. The acid-type montan wax had a drop point of 172-l81 F. (ASTM D-566- 49), a congealing point of 167-176 F. (ASTM D-938- 48), acid value of 115-130 (ASTM D-1386-557) and a saponification value of 135-155 (ASTM D-l387-557).

TABLE-COMPOSITIONS AVNVEXPROPE RTIES F CASTING Weight percent Composition l 2 3 4 5 6 Microcrystalline wax l 25 20 10 5 0 Paraflin wax 2 0 5 10 16 20 Paraffin wax 3 25 25 25 25 25 25 Chlorinated polyphenyl 38 38 38 38 38 38 Acid type Montan wax. 10 10 10 10 10 10 Stearlc acid 2 2 2 2 2 2 Total 100 100 100 100 100 100 Properties: 8

Penetration, 100 g.:

77 3 4 3 1 1 9 13 12 9 7 ll 26 27 26 20 16 19 162 145 134 135 156 70 67 6; 61 58 56 Melting point, F. 176 177 17,4. 165 164 161 Expansion, percent 8. 0 7. 8 8.3 8.4 8. 7 8. 8 Percent ash 0. 02

1 Sun Oil Company microcrystalline wax 985B. 1 Sun Oil Company paraflin wax 5512.

3 Sun Oil Company paraflin wax 4412. 4 ASTM D-1321.

ASTM 13-446.

' ASTM D-127.

Volume.

B Compositions 2 and 3 have modulus of ruptures of 909 p.s.i. and 928 p.s.i. respectively.

The ASTM tests for the aforementioned properties are as follows unless otherwise noted: penetration, -D- 1321; oil content, D-721; viscosity, D-446.

Composition 1, shown in the accompanying table, was prepared by accurately weighing 25 parts of the aforementioned microcrystalline wax, 25 parts of the aforementioned paraffin wax having a melting point of 145 F., 38 parts of the aforementioned solid chlorinated polyphenyl, 10 parts of the aforementioned acid type montan wax and 2 parts of the aforementioned stearic acid and placing the materials into a container. The container was then placed into an oven maintained at 250 F. When all the components were melted, the container was removed and the material in the container was stirred to insure a homogeneous blend. The container and its contents were then allowed to cool to 175 F. with constant stirring. The molten blend was then poured into a pressure casting cylinder. The latter is a pressure vessel with a movable piston. The application of pressure on the piston forces the blend in the vessel out through an opening which has a shut off device. The cylinder and its contents were maintained overnight at 136-140 F. in an oven.

A mold was placed in a suitable laboratory press and clamped with a force of 10,000 p.s.i.g. to prevent the mold from separating during casting. The pressure casting cylinder was removed from the oven and screwed into the mold. The cylinder was pressurized to 150 p.s.i. and was maintained at that pressure for 30 seconds. The pressure was then reduced and the casting cylinder was removed. The mold was taken out of the press and opened. The molded article had excellent surface finish and mold detail. The entire procedure; i.e., injection and cooling, required only 57 seconds.

Compositions 2-6 were prepared and tested in a manner like Composition 1 except that the weights of the components of the compositions were as shown in the accompanying table.

The data in the accompanying table demonstrate that the refined petroleum wax can be used as a major component of investment casting wax. Furthermore, the data indicate that despite the substantial amount of refined petroleum wax in the casting wax, the penetration at 100 F. of the latter is below 15 and the expansion is below 10%. Such a low penetration value indicates that the wax article is hard at a warm temperature and therefore can be handled and invested with ceramic forming materials without causing deformations on the wax surface. Low shrinkage means minimum dimension corrections are necessary when preparing the wax article.

The melting points and viscosities shown in the accompanying table indicate that the compositions are suitable for use in injection equipment.

Satisfactory investment casting Waxes can be prepared containing other quantities of refined petroleum waxes and other components; i.e., solid chlorinated polyphenyls, acid type montan waxes and stearic acid, within the limits herein specified, with similar results being obtained.

The invention claimed is:

1. An investment casting wax composition consisting essentially of:

(a) 35-65 weight percent of refined petroleum wax;

(b) 25-55 weight percent of solid chlorinated polyphenyl;

(c) 5-15 weight percent of acid type montan wax; and

(d) 0.1-5.0 weight percent of stearic acid; said composition having low strinkage and low penetration.

2. Composition according to claim 1 wherein the composition contains about 40-60 weight percent of refined petroleum wax.

3. Composition according to claim 1 wherein the composition contains about 45-55 Weight percent of refined petroleum wax.

4. Composition according to claim 1 wherein the penetration at F. of said investment casting wax composition is less than 15.

5. Composition according to claim 4 wherein the expansion of said investment casting wax composition is less than 9% 6. Composition according to claim 1 wherein the refined petroleum wax is selected from the following group: paraffin wax, microcrystalline wax, or mixture of paraffin wax and microcrystalline wax.

7. Composition according to claim 6 wherein the ratio of the paraifin wax to the microcrystalline wax in said mixture is about 0.05-1.0.

8. Composition according to claim 6 wherein the melting point of the paraffin wax is at least 127 F. and the melting point of the microcrystalline wax is at least 151 F.

9. Composition according to claim 8 wherein said paraflin waxs penetration at 77 F. is less than 33 and said microcrystalline waxs penetration at 77 is less than 21.

10. Composition according to claim 8 wherein the acid type montan waxs melting point is 170-185 F.

11. Composition according to claim 8 wherein the refined petroleum wax is selected from the following group:

paraflin wax with a melting point of ISO-156 F.;

microcrystalline wax with a melting point of 175- mixture of said paraflin wax and said microcrystalline wax.

12. Composition according to claim 11 wherein the ratio of the paraflin wax to the microcrystalline wax in said mixture is 0.05-1.0.

13. Composition according to claim 1 wherein the composition consists essentially of:

(a) 40-60 weight percent of a refined petroleum wax selected from the following group: paraffin wax having a melting point of -156" F.. microcrystalline wax having a melting point of 175-197 F., a mixture of said paraffin wax and said microcrystalline wax wherein said mixture the ratio of paraflin wax to microcrystalline wax is 0.2-0.6;

(is) 35-45 weight percent of solid chlorinated polyphenyl;

(c) 8-12 weight percent of acid type montan wax having a melting point of -185 F.; and

(d) (1.1-5.0 weight percent of stearic acid,

14. Composition according to claim 13 wherein said parafiin waxs penetration at 77 F. is less than 15 and slaid microcrystalline waxs penetration at 77 F. is less t an 12.

8 15. A wax replica consisting essentially of: References Cited (a) 35-65 weight percent of refined petroleum wax; UNITED STATES PATENTS 2 welght percent f sohd chlormated p y- 2,469,611 5/1949 Rose P 5 3,263,286 8/19'66 Watts 106-38.8 Weight percent of and yp montan wax; a 3,316,105 4/1967 .Feagm 106 27O (d) 0. 1-5 .0 weight percent of stearic acid, 7 said replica having a penetration at 100 F. of less than OTHER REFERENCES 15. v v H. W. Booth: Pattern Waxes For Investment Cast- 16. The wax replica of claim 15 wherein the replica 1o Foundary Trade Journal, Decemconsists essentially of: her 1962' (a) 40-60 weight percent of refined petroleum Wax; MORRIS LIEBMAN Primary Examiner b35-45 ht tf 1n 1' ghenyl; Wag Percen 1 ch mated P. R. MICHL, Assistant Examiner (c) 8-12 weight percent of acid type rnontan wax; and 15 US Cl.

(d) l-3 weight percent of stearic acid. 106 38.7, 38.8, 270 

